(1) Field of Invention
This invention relates to nonaqueous liquid fabric treating compositions. More particularly, this invention relates to nonaqueous liquid laundry detergent compositions which are stable against gelation, are easily dispersible and are easily pourable and to the use of these compositions for cleaning soiled fabrics.
(2) Discussion of Prior Art
Liquid nonaqueous heavy duty laundry detergent compositions are well known in the art. For instance, compositions of that type may comprise a liquid nonionic surfactant in which are dispersed particles of a builder, as shown for instance in the U.S. Pat. Nos. 4,316,812, 3,630,929 and 4,264,466 and British Pat. Nos. 1,205,711, 1,270,040 and 1,600,981.
The related pending applications assigned to the common assignee are:
Ser. No. 680,630 filed Dec. 12, 1984 describes a concentrated stable nonaqueous fabric softener composition comprising hexylene glycol alone or in combination with a lower alkanol or another glycol or glycol ether, or mixtures thereof as a liquid carrier for cationic fabric softeners, especially the quaternary ammonium and imidazolinium cationic softeners. The concentrated compositions may contain up to 60% by weight of the cationic compound and may additionally include up to 15% by weight of a nonionic surfactant.
Ser. No. 687,815 filed Dec. 31, 1984 describes a nonaqueous liquid nonionic surfactant detergent composition comprising a suspension of a builder salt and containing an acid terminated nonionic surfactant (e.g., the reaction product of a nonionic surfactant and succinic anhydride) to improve dispersibility of the composition in an automatic washing machine.
Ser. No. 687,815 filed Dec. 31, 1984 describes a nonaqueous liquid nonionic surfactant detergent composition comprising a suspension of builder salt and containing an alkylene glycol mono-alkyl ether as a viscosity and gel control agent to improve dispersibility of the composition in an automatic washing machine.
Ser. No. 597,793 filed Apr. 6, 1984 describes a nonaqueous liquid nonionic surfactant detergent composition comprising a suspension of polyphosphate builder salt and containing an alkanol ester of phosphoric acid to improve stability of the suspension against settling in storage.
Liquid detergents are often considered to be more convenient to employ than dry powdered or particulate products and, therefore, have found substantial favor with consumers. They are readily measurable, speedily dissolved in the wash water, capable of being easily applied in concentrated solutions or dispersions to soiled areas on garments to be laundered and are non-dusting, and they usually occupy storage space. Additionally, the liquid detergents may have incorporated in their formulations materials which could not stand drying operations without deterioration, which materials are often desirably employed in the manufacture of particulate detergent products. Although they are possessed of many advantages over unitary or particulate solid products, liquid detergents often have certain inherent disadvantages too, which have to be overcome to produce acceptable commercial detergent products. Thus, some such products separate out on storage and others separate out on cooling and are not readily redispersed. In some cases the product viscosity changes and it becomes either too thick to pour or so thin as to appear watery. Some clear products become cloudy and other gel on standing.
The present inventors have been involved in studying the behavior of nonionic liquid surfactant systems with particulate matter suspended therein. Of particular interest has been nonaqueous built laundry liquid detergent compositions and the problem of settling of the suspended builder and other laundry additives as well as the problem of gelling associated with nonionic surfactants. These considerations have an impact one, for example product stability, pourability and dispersibility.
It is known that one of the major problems with built liquid laundry detergents is their physical stability. This problem stems from the fact that the density of the solid particles dispersed in the nonionic liquid surfactant is higher than the density of the liquid surfactant.
Therefore, the dispersed particles tend to settle out. Two basic solutions exist to solve the settling out problem: increase nonionic liquid viscosity and reduce the dispersed solid particle size.
It is known that suspensions can be stabilized against settling by adding inorganic or organic thickening agents or dispersants, such as, for example, very high surface area inorganic materials, e.g. finely divided silica, clays, etc., organic thickeners, such as the cellulose ethers, acrylic and acrylamide polymers, polyelectrolytes, etc. However, such increases in suspension viscosity are naturally limited by the requirement that the liquid suspension be readily pourable and flowable, even at low temperature. Furthermore, these additives do not contribute to the cleaning performance of the formulation.
Grinding to reduce the particle size provides the following advantages:
1. Specific surface area of the dispersed particles is increased, and, therefore, particle wetting by the nonaqueous vehicle (liquid nonionic) is proportionately improved.
2. The average distance between dispersed particles is reduced with a proportionate increase in particle-to-particle interaction. Each of these effects contributes to increase the rest-gel strength and the suspension yield stres* while at the same time, grinding significantly reduces plastic viscosity.
The yield stress is defined as the minimum stress necessary to induce a plastic deformation (flow) of the suspension. Thus, visualizing the suspension as a loose network of dispersed particles, if the applied stress is lower than the yield stress, the suspension behaves like an elastic gel and no plastic flow will occur. Once the yield stress is overcome, the network breaks at some points and the sample begins to flow, but with a very high apparent viscosity. If the shear stress if much higher than the yield stress, the pigments are partially shear-deflocculated and the apparent viscosity decreases. Finally, if the shear stress is much higher than the yield stress value, the dispersed particles are completely shear-deflocculated and the apparent viscosity is very low, as if no particle interaction were present.
Therefore, the higher the yield stress of the suspension, the higher the apparent viscosity at low shear rate and the better is the physical stability against settling of the product.
In addition to the problem of settling or phase separation, the nonaqueous liquid laundry detergents based on liquid nonionic surfactants suffer from the drawback that the nonionics tend to gel when added to cold water. This is a particularly important problem in the ordinary use of European household automatic washing machines where the user places the laundry detergent composition in a dispensing unit (e.g. a dispensing drawer) of the machine. During the operation of the machine the detergent in the dispenser is subjected to a stream of cold water to transfer it to the main body of wash solution. Especially during the winter months when the detergent composition and water fed to the dispenser are particularly cold, the detergent viscosity increases markedly and a gel forms. As a result some of the composition is not flushed completely off the dispenser during operation of the machine, and a deposit of the composition builds up with repeated wash cycles, eventually requiring the use the flush the dispenser with hot water.
The gelling phenomenon can also be a problem whenever it is desired to carry out washing using cold water as may be recommended for certain synthetic and delicate fabrics or fabrics which can shrink in warm or hot water.
The tendency of concentrated detergent compositions to gel during storage is aggravated by storing the compositions in unheated storage areas, or by shipping the compositions during winter months in unheated transportation vehicles.
Suspensions of builder salts, for example, sodium tripolyphosphates, in nonaqueous liquid nonionic surfactant laundry detergent compositions are characterized by a plastic viscosity and a yield stress value and an apparent viscosity. The compositions which exhibit a high plastic viscosity also exhibit a high yield stress value and are physically stable. However, in compositions which have a high plastic viscosity, it is found that gel formation is enhanced when the compositions are added to water. Normally reducing the plastic viscosity dramatically reduces the yield stress value and substantially reduces the physical stability of the composition. Further, for the composition to be physically stable the apparent viscosity must be high. However, high apparent viscosity usually adversely affects the dispersibility of the composition in cold water.
Partial solutions to the gelling problem in aqueous, substantially builder free compositions have been proposed, for example, by diluting the liquid nonionic with certain viscosity controlling solvents and gel-inhibiting agents, such as lower alkanols, e.g. ethyl alcohol (see U.S. Pat. No. 3,953,380), alkali metal formates and adipates (see U.S. Pat. No. 4,368,147), hexylene glycol, polyethylene glycol, etc. and nonionic structure modification and optimization. In addition, these two patents each disclose the use of up to at most about 2.5% of the lower alkyl (C.sub.1 -C.sub.4) etheric derivatives of the lower (C.sub.2 -C.sub.3) polyols, e.g. ethylene glycol, in these aqueous liquid builder-free detergents in place of a portion of the lower alkanol, e.g., ethanol, as a viscosity control solvent. To similar effect are U.S. Pat. Nos. 4,111,855 and 4,201,686. However, there is no disclosure or suggestion in any of these patents that these compounds, some of which are commercially available under the tradename Cellosolve (Registered Trademark), could function effectively as viscosity control and gel-preventing agents for nonaqueous liquid nonionic surfactant compositions, especially such compositions containing suspended builder salts, such as the polyphosphate compounds, and especially particularly such compositions which do not depend on or require the lower alkanol solvents as viscosity control agents.
As an example of nonionic surfactant modification for gel inhibition one particularly successful result has been achieved by acidifying the hydroxyl moiety end group of the nonionic molecule. The advantages of introducing a carboxylic acid at the end of the nonionic include gel inhibition upon dilution; decreasing the nonionic pour point; and formation of an anionic surfactant when neutralized in the washing liquor. Nonionic structure optimization has centered on the chain length of the hydrophobic-lipophilic moiety and the number and make-up of alkylene oxide (e.g. ethylene oxide) units of the hydrophilic moiety. For example, it has been found that a C.sub.13 fatty alcohol ethoxylated with 8 moles of ethylene oxide presents only a limited tendency to gel formation.
Nevertheless, improvements are desired in both the stability, gel inhibition and dispersibility of nonaqueous liquid fabric treating compositions.